Combines past tense -(았/었/였)- with prospective modifier -(으)ㄹ and bound noun 것 to express speculation about what would have happened or what someone would have done.

• •Speculation: "날씨가 좋았으면 갔을 거예요" (If the weather had been good, I would have gone)
• •Assumption: "아팠을 거예요" (They would have been sick / They must have been sick)